Dynamic features of short-range interaction force and adhesion in solutions

A dynamic procedure in atomic force microscopy was employed to investigate the adhesion and the short-range interaction force between a silica sphere and a mica plate in pure water and LiCl and CsCl solutions. The long-range interaction force was independent of the dynamic procedure of measuring. On the other hand, the apparent short-range force curve and the adhesive force depended on the approach velocity of surfaces and the contact time, respectively, and both of them depended on the history of the contact of surfaces prior to the measurement, as well as the electrolyte concentration and cationic species. These results indicated that there exist two kinds of structured layers on the surface; the thin but firm primary layer composed of water molecules, cations, and hydrated cations adsorbed onto the surface and the thick but fragile secondary layer outside the primary layer.